Time synchronization method with trusted beacons and distributed fiber sensing

Abstract

A method for time synchronization using distributed fiber optic sensing (DFOS) that employs several trusted time beacons that are attached to the DFOS sensing fiber which in turn is connected to the DFOS interrogator. The beacons transmit their signal via two different mediums, (1) wirelessly to sensor nodes in the coverage area, and (2) through vibrations on fiber to the DFOS/DAS system located at a trusted area such as the central office. Wireless broadcast to nearby sensors includes a timestamp and beacon ID. All the sensors in the field use one of the beacons in their vicinity (the one with the strongest signal) as their time reference and send the data back with the corresponding beacon index.

The invention claimed is: 
     
       1. A method for distributed fiber optic sensing (DFOS) systems comprising:
 providing a DFOS system including
 a length of optical sensor fiber; 
 an optical interrogator configured to generate optical pulses, introduce the generated optical pulses into the optical sensor fiber, and receive backscattered optical signals in response to the introduced optical pulses; and 
 an analyzer that analyzes the backscattered optical signals and determines vibrational activity occurring at locations along the length of the optical sensor fiber; 
 
 providing a plurality of beacons at a respective plurality of locations along the length of the optical sensor fiber, the plurality of beacons including
 vibrators configured to generate mechanical vibrations; and 
 wireless transceivers configured to transmit and receive wireless signals; 
 
 wherein the plurality of beacons generate mechanical vibrations, such vibrations are detected by the DFOS system. 
 
     
     
       2. The method of  claim 1  further comprising:
 providing a plurality of sensor nodes located within a wireless range of at least one of the plurality of beacons, the plurality of sensor nodes including one or more sensors configured to sense one or more environmental conditions, the plurality of sensor nodes configured to provide the sensed environmental conditions to the at least one of the plurality of beacons wirelessly. 
 
     
     
       3. The method of  claim 2  wherein the at least one of the beacons communicates a broadcast synchronization message including timestamp and beaconID information to the plurality of sensor nodes wirelessly. 
     
     
       4. The method of  claim 3  wherein the plurality of sensor nodes that receive the timestamp and beaconID information are configured to synchronize locally in response to receiving the synchronization message including the timestamp and beaconID information. 
     
     
       5. The method according to  claim 4  wherein the plurality of sensor nodes are configured to adjust a clock delay of sensing data according to received timestamps and synchronize the plurality of sensor nodes within an entire coverage area. 
     
     
       6. The method according to  claim 3  wherein the at least one of the beacons encodes the synchronization message including the timestamp and beaconID in a vibration code and communicates the vibration encoded synchronization message mechanically to the DFOS system.